Studies have shown that watching television induces low alpha waves in the human brain. Alpha waves are brainwaves between 8 to 12 HZ. and are commonly associated with relaxed meditative states as well as brain states associated with suggestibility.
While Alpha waves achieved through meditation are beneficial (they promote relaxation and insight), too much time spent in the low Alpha wave state caused by TV can cause unfocussed daydreaming and inability to concentrate. Researchers have said that watching television is similar to staring at a blank wall for several hours..
a magazine, the brainwaves reverted to Beta waves.
Research indicates that most parts of the brain, including parts responsible for logical thought, tune out during television viewing. The impact of television viewing on one person's brain state is obviously not enough to conclude that the same consequences apply to everyone, but research has repeatedly shown that watching television produces brainwaves in the low Alpha range.
Advertisers have known about this for a long time and they know how to take advantage of this passive, suggestible, brain state of the TV viewer. There is no need for an advertiser to use subliminal messages. The brain is already in a receptive state, ready to absorb suggestions, within just a few seconds of the television being turned on. All advertisers have to do is flash a brand across the screen, and then attempt to make the viewer associate the product with something positive.
http://appliedneurotec.com/neuroscience/effects-of-tv-on-your-brain/